In the drafting of line drawings such as employed for parts layout, architectural renderings, and the like a variety of highly specialized tools are commonly employed. First of all, a drafting board or table with a straight edge or its equivalent is required. Then, an assortment of drafting tools such as T-squares, rules, compasses, protractors, and various triangles of different angles are employed. When a draftsman uses such tools in laying out a drawing, much time is spent in picking up and setting down the various tools used at different times to draw lines at different angles, circles, and the like. In addition, since these various drafting tools, particularly as used by professional draftsmen and architects, must be accurate, they are relatively expensive.
Even with the variety of conventional tools which are mentioned above, the ability to quickly and accurately perform many functions required of a draftsman often is not facilitated by the tools themselves, but the draftsman must make various mental calculations. One commonly encountered layout problem which is solved by the centerline rule disclosed in the above-mentioned copending application is that of drawing a line of a particular length with a given reference point as a center point. This rule has a half scale and full scale with centered zero-point references displayed on the scales. These are interconnected by a perpendicular center line. Consequently, the tool permits a line of given length centered on a given point to be accurately and quickly determined and drawn, all in a single operation without any additional mathematical calculations or scale estimations. In addition, by employing the center line and windows, a line can be drawn across a reference line of known length on either side of and perpendicular to the reference line all in a single operation.
Various composite drafting tools employing lines on them at different angles, and many incorporating protractors or other angle determining devices, have been developed in the past. One example is illustrated in the Patent to VanNess, U.S. Pat. No. 1,154,673, issued Sept. 28, 1915. This patent discloses a forty-five degree right triangle with ruler scales scribed or printed along both legs of the triangle. In addition, a variety of lines at different angles are shown on the face of the triangle to assist its use in layout. A rotatable protractor is mounted in the center, and throughout the protractor and the triangle itself a large number of small holes (to accommodate the tip of a pencil) are placed with printed indicia adjacent them to permit the drawing of circles of various diameters by use of the tool. The rotatable protractor construction obviously makes this a relatively expensive tool. In addition, the placement of the holes for drawing circles is not convenient to use; and, since there is no scale directly adjacent the holes, the entire tool must be searched each time for the designation of the radius or diameter of the circle to be drawn. There is no center line or zero-point reference for facilitating drafting with this tool, so that mental calculations still must be made whenever it is used.
The Elger Patent, U.S. Pat. No. 3,289,299, is directed to a protractor having a configuration in which the protractor itself is printed or etched onto the face of a trapezoidal shaped base member. The top of the trapezoid is parallel to the bottom of the trapezoid which, in turn, serves as the base line for the protractor. The top and bottom are interconnected by converging oblique sides which make an angle of sixty degrees with respect to the base line of the protractor. This is an angle which is commonly encountered in drafting, so that the outside edges of the tool may be used directly to lay out lines at this angle. Also scribed on the face of the protractor are a large number of concentric circles each having a small hole on it to permit use of the tool to draw arcs or circles having the desired radii marked on the tool adjacent each of the concentric lines. While the tool of this patent is capable of somewhat specialized use as a protractor, it is not as universal a tool as the one disclosed in the VanNess Patent. Many of the shortcomings present in VanNess are also present in the tool of the Elger Patent.
Efforts to provide a tool which acts as a straight edge ruler and also includes the function of a protractor are disclosed in the Patents to Bryson U.S. Pat. No. 846,006, issued Mar. 5, 1907; and Owen, Jr., U.S. Pat. No. 1,808,705, issued June 2, 1931. The Patent to Bryson discloses an elongated ruler having both longitudinal and perpendicular transverse spaced lines on it. In addition, a protractor, with its origin near the center of one of the edges of the rule, is provided; and lines at various angles also are placed on the face of the ruler to facilitate its use as a layout drafting tool. The various lines on this tool permit it to be used to draw a variety of straight lines at various angles with respect to one another so that it greatly facilitates many layout operations. The tool, however, cannot be used for drawing and establishing curved lines. Thus, a compass or other type of device for accomplishing this is necessary. In addition, there is no provision for multiple scale measurements or for center line layouts which do not involve additional mathematical computations and measurements.
The Owen, Jr. Patent is similar to the ruler of Bryson except it has a rotatable eyelet mounted in it at the center point of circles which may be drawn by placing a pencil through a hole located at a measured distance from the eyelet. Thus, this tool is capable of use as a beam compass as well as a ruler and straight edge. The tool itself is rectangular and has a graduated English scale along one edge and a metric scale along the opposite edge on the long side. A protractor is also scribed on the face of the rule and has its origin at the center point of one of the edges of the tool.
It is desirable to provide a drafting tool for use in making a variety of layout drawings which overcomes the disadvantages of the various tools of the prior art mentioned above and which also permits additional functions to be performed directly by the user without requiring him to resort to the use of multiple tools of the type commonly employed by mechanical and architectural draftsmen.